§ 1.1 Field of the Invention
The present invention generally concerns the design of an air purifier using plasma torches to carry out sterilization. It involves the design of a new magnetized torch module and a controlling air valve. Two torches are run alternatively to eliminate the cooling requirement; the controlling air valve guides the airflow from the off-torch module to pass through the torch of the on-torch module. The plasma effluent of the torch carries abundant atomic oxygen, which can effectively kill all kind of microbes. Therefore, the airflows through both torch modules are treated even though there is only one torch used at any time. Application of the device is for purifying as well as sterilizing air.
§ 1.2 Background
A torch module described in the article S. P. Kuo, et al., “Design and electrical characteristics of a modular plasma torch,” IEEE Trans. Plasma Sci. Vol. 27, no. 3, pp. 752-758, June, 1999, New Jersey; and in the U.S. Patent S. P. Kuo, et al., U.S. Pat. No. 6,329,628, “Methods and Apparatus for Generating a Plasma Torch,” December 2001, (“the '628 patent”) produces a plasma torch via arc discharge, which is stabilized by introducing a flow through the discharge. The torch module can be run in low frequency (e.g., 60 Hz) periodic mode to produce low temperature non-equilibrium air plasma. The required discharge voltage is proportional to the gap between the two (concentric) electrodes. Thus the gap is usually small. The gas flow rate through the gap is proportional to the cross sectional area of the ring-shaped gap, which is the product of the gap and the periphery length of the ring gap. The periphery length of the ring gap can be increased by increasing the radial size of the torch module. A torch module is designed with the inner diameter of the outer electrode to be 20 mm. The central electrode is a spline copper disk with a diameter of 18 mm, i.e., the side surface of the disk is carved with grooves. The spline structure improves the performance of the discharge and increases the airflow for a fixed gap. A schematic of the torch module is presented in FIG. 1, in which photos of the torch frame (b), central electrode (c), and side view (d) and top view (e) of the module are also shown. An air purifier employing two torch modules, running alternately to generate plasma for air treatment, is devised. In the device a synchronous controlling air valve is designed so that the airflows through the two torch modules are always treated by the torch, one in the torch and the other one crossing the plasma effluent of the torch.
The advantages of using two torches and running alternately are 1) eliminating the cooling requirement of the torch module and 2) doubling the airflow rate and thus the air treating rate.
The torch in the device produces non-equilibrium plasma, which has a good usage of the electron plasma energy, gained from the discharge, to produce reactive oxygen species (ROS), rather than to heat the airflow. ROS (particularly, the reactive atomic oxygen (RAO)) are effective in killing microorganisms including the toughest biological agents, bacterial spores, such as Anthrax (See, e.g., the articles: H. W. Herrmann et al., “Decontamination of chemical and biological warfare (CBW) agents using an atmospheric pressure plasma jet (APPJ),” Phys. Plasma, Vol. 6, pp. 2284-2289, May 1999, New York (hereafter referred to as “the Herrmann article”); and Wilson Lai et al., “Decontamination of Biological Warfare Agents by a Microwave Plasma Torch”, Phys. Plasmas, Vol. 12, 023501 (1-6), February 2005, New York (hereafter referred to as “the Lai article”)).